Conventional printers have ejected ink droplets through nozzles in order to form ink dots on a printing medium. One such printer known in the art alternates between an operation to eject ink droplets from the nozzles and to form ink dots while moving the print head possessing the nozzles in a main scanning direction, and an operation to convey the printing medium in a sub scanning direction orthogonal to the main scanning direction. Further, in order to prevent the occurrence of periodic streaks (called “banding”) in the main scanning direction, there has also been proposed a technique for varying the conveying distance so that the distance of each main scanning operation is different from the distance used in the previous main scanning operation (Japanese Patent Application Publication No. 2006-27131, for example).